Methods for modifying the rheology of polymers

ABSTRACT

The disclosure relates to a method for modifying the rheology of a polymer and a polymeric composition obtained by the method. The composition comprises at least one organic peroxide and water in emulsion form. The polymer may comprise a polyolefin. The method comprises extruding a molten polymer and the composition and removing volatile compounds from the molten polymer.

BACKGROUND OF INVENTION Technical Field

The present disclosure relates to a method for modifying the rheology ofpolymers as well as to polymeric compositions obtained by such a method.

Background Art

Polymers, such as for example polyolefins produced with Ziegler-Nattacatalysts, may have high molecular weights and broad molecular weightdistributions, thus having a high melt viscosity, which is evidenced bya low Melt Flow Rate (MFR). These properties are undesired whenprocessing polyolefins in some product applications, such as for examplemolding, films and fibers applications. Therefore, methods have beendeveloped for reducing the polyolefin molecular weight and for narrowingthe molecular weight distribution by changing the rheology of thepolyolefin, for example by reducing the viscosity of the polyolefin inliquid phase. A narrow molecular weight distribution and an increase inmelt flow rate are responsible for improved flow properties ofpolyolefins. This change in the rheology for improving the flowproperties of polyolefins, thus making the polyolefins more suitable forsome product applications, is described as “modifying” the rheology ofthe polyolefins. The viscosity reduction is also described as polymer“visbreaking” or “degradation”. Viscosity reduction is conventionallyapplied, for example to polypropylene.

In the present application, rheological modification is intended toindicate any rheological modification, including “visbreaking” andcross-linking of polymers, which may also be accompanied by degradationside-reactions. Cross-linking is conventionally applied, for example, topolyethylene.

It is known to use organic peroxides for the rheological modification ofpolyolefins.

A known process for visbreaking polyolefins is extrusion performed at atemperature of about 190° C.-260° C. in the presence of an organicperoxide compound. An example of this process is described in documentAU 5141785 A, which relates to a process for the controlled reduction ofaverage molecular weight and alteration of molecular weight distributionof C3-C8 alpha-monoolefin homopolymers or copolymers by adding aperoxide, such as such as 2,5-dimethyl-2,5-di(t-butylperoxy)hexane,continuously at a programmed cyclic rate to the polymer or copolymer andheating the mixture in a melt extruder.

However, due to their organic nature, pure organic peroxides are veryunstable, volatile and dangerous species with high risk of ignition orexplosion in case of uncontrolled increase of temperature and thereforerequire particular handling precautions. This behavior may beincompatible with the rules for transportation and storage and/orrequire special efforts for safe handling and storage, thus making theuse of pure organic peroxides very expensive and technically complex.Also, the use of pure organic peroxides in an extrusion process, whichis performed at high temperatures, is still more dangerous.

Accordingly, safe handling is a significant concern with organicperoxides and the use of pure organic peroxides in an extrusion processis problematic.

In the attempt of solving the issues relating to storage andtransportation, organic peroxides have been diluted with mineral oil. Bydiluting the organic peroxide, less restricted peroxide product safetyclasses may be obtained. Also, dispersion of an organic peroxide in apolymer, for example a polyolefin, may be assisted by the dilution ofthe organic peroxide in mineral oil. However, although the organicperoxide may lower the viscosity of polyolefins and produce a relativelynarrow molecular weight distribution, the organic peroxide leaves odorin the polyolefin from decomposition products. Furthermore, polyolefinyellowing may also be induced by the organic peroxide, requiring a lowerextrusion temperature and/or stabilizers to eliminate or minimize thecoloration. Also, the mineral oil causes several additional unwantedside effects impacting the polymer properties. For example, currentlyavailable mineral oil diluted organic peroxides provide no safety issue,allowing greater storage capacities with respect to those obtainablewith pure organic peroxides, but introduce solvent into the polymer,which may disturb the polymer conversion into the final polymer productsand may lead to additional degradation of by-products during theperoxidic reaction in the extruder. These degradation and by-productsinduce high volatiles organic compounds (VOCs) and undesired odors tothe polymer and the final polymer product.

Another form in which peroxides may be used is that of aqueous peroxideemulsions. For example, document WO 00/42078 A1 describes aqueousperoxide emulsions used in polymerization reactions with the aim ofbroadening the class of anti-freeze additives which may be added to thepolymer and of ensuring safety. The aqueous peroxide emulsions ofdocument WO 00/42078 A1 contain an emulsifier system comprising acopolymer of an α,β-unsaturated dicarboxylic acid and a C8-24 α-olefin,the acid groups of which are esterified with an ethoxylated alcoholhaving a degree of ethoxylation of 1-45, as well as an ethoxylated fattyalcohol with an HLB value greater than 16. Document WO 00/42078 A1states that these peroxide emulsions can be used in variouspolymerization reactions, including the curing of unsaturated polyesterresins, and polymer modification reactions, including degradation,cross-linking, and grafting reactions. The peroxide emulsions ofdocument WO 00/42078 A1 are stated to be pre-eminently suited for use ina polymerization process as (one of) the polymerization initiator (s) inthe polymerization of vinyl chloride alone or in admixture with up to40% by weight of one or more ethylenically unsaturated monomerscopolymerizable therewith, oligomers and (co) polymers of theaforementioned monomers, and mixtures of two or more of these monomers,oligomers, and polymers. However, no example of polymer modificationreaction is described in this document.

The known methods for modifying the rheology of polymers using organicperoxides, independently of the form in which organic peroxides are used(non-diluted organic peroxides, organic peroxides diluted in mineral oiland aqueous peroxide emulsions), do not allow to obtain polymers havinga sufficiently low level of volatile organic compounds and asatisfactory low odor and/or color formation.

For example, in all known methods for modifying the rheology ofpolymers, an excessive content of volatile organic compounds is stillfound in the extruded polymer.

Further, in all known methods for modifying the rheology of polymers,degradation and color formation may be also caused by the conventionalprocess required for deactivating active catalyst sites after thepolymerization. For this purpose, in conventional methods, a separatedeactivation vessel is arranged downstream of the polymerizationreactor. The deactivation is performed in the deactivation vessel withsteam injected through the polymer powder bed. However, when thedeactivation is either insufficient or non-uniform, the polymer has highpotential for corrosion of the equipment, thus increasing thedegradation potential of the polymer, with impacts on stabilizerconsumption and color formation.

In view of the above, there is still the need of developing methods formodifying the rheology of a polymer, such as for example polypropyleneand polyethylene, in a safe manner and resulting in a polymer havingimproved quality, in particular in terms of contents of volatile organiccompounds, and odor and color formation. Additionally, there is stillthe need of providing methods for modifying the rheology of a polymernot requiring a further, separate deactivation step following thepolymerization step.

SUMMARY OF INVENTION

The Applicant has surprisingly found that by using a compositioncomprising an organic peroxide emulsified with water, by contacting apolymer with the composition under extrusion conditions and by removingvolatile compounds generated during extrusion from the molten polymer,not only safe transport and storage of the organic peroxide is ensured,but, in addition, the rheology of the polymer may be modified whilereducing the generation of degradation and by-products in the polymer,which results in less VOCs, lower odor concentrations in the polymer andreduced color formation.

Recently, the inventors tested aqueous organic peroxide emulsions in anextrusion process comprising a step of removing volatile compounds fromthe molten polymer and were surprised to find that aqueous organicperoxide emulsions worked significantly and unexpectedly better thanwould have been predicted by using a corresponding amount of water andorganic peroxide without emulsifying the organic peroxide with water.Also, the inventors were surprised to find that removing volatilecompounds from the molten polymer unexpectedly resulted in a significantreduction of the generation of degradation and by-products in thepolymer and in an improved degassing of the generated degradation andby-products.

According to a first aspect thereof, the present disclosure relates to amethod for modifying the rheology of a polymer, comprising extruding amolten polymer and a composition comprising at least one organicperoxide and water in emulsion form, and removing volatile organiccompounds and moisture from the molten polymer.

According to one or more embodiments, the method comprises removingorganic volatile compounds resulting from the degradation of the organicperoxide and/or of the polymer.

According to one or more embodiments, the residual volatile organiccompounds are less than 1100 mVs, for example less than 1000 mVs.According to one or more embodiments, the residual volatile organiccompounds are less than 700 mVs, for example from 400 mVs to 650 mVs.

According to one or more embodiments, the method also comprises removingmoisture from the molten polymer.

Extruding a molten polymer and a composition comprising at least oneorganic peroxide and water in emulsion form (i.e., an emulsion of atleast one organic peroxide and water) is intended to indicate extrudinga molten polymer in the presence of the emulsion. According to one ormore embodiments, extruding a molten polymer and the emulsion may beperformed by extruding the polymer, which may be for example in aninitial powder or pellet form, adding the above-mentioned emulsion tothe polymer, and melt extruding the polymer in the presence of saidemulsion. Adding the emulsion to the polymer may be for exampleperformed before or during the extrusion of the polymer.

Such a method as defined in the first aspect of the disclosure iseffective for the rheological modification of polymers, for example forpolymer degradation and/or cross-linking, without resulting inintolerable levels of odor and/or color and without requiring specialhandling precautions because storage, transportation and use are safe.For example, a storage capacity of above 1000 L may be obtained, whichis convenient for storing materials intended to be used in highthroughput extrusion plants.

Extruding may be performed in an extruder or in any other meltprocessing device. In both cases, extruding is performed under extrusionconditions. The water of the emulsion, under extrusion conditions, is invapor form and, when removed, for example by venting the extruder, mayextract undesired deactivated species and degradation products from themolten polymer in an enhanced manner. The enhanced degassing ofundesired degradation products and by-products obtained by removing thevapor under extrusion conditions further reduces both VOCs and odorconcentrations. As a consequence, an improved polymer degassing may beobtained during the rheological modification of the polymer. Thus, themethod according to one or more embodiments of the present disclosureresults not only in a modification of the rheology of the polymer bycontacting the emulsion with the molten polymer under extrusionconditions, but also in an effective extraction of deactivated speciesand degradation products from the molten polymer.

Further, the use of water removes the need for mineral oil and theunwanted side effects thereof.

Also, water may deactivate the active catalyst sites remaining in thepolymer. Therefore, by using water in the extruder, polymer deactivationcan be accomplished in a single apparatus, i.e., in the extruder,without requiring a specific deactivation apparatus. By providing asufficient mixing in the extruder along with the emulsion, thedeactivation may be uniform and may be obtained in an efficient manner.

Thanks to the simultaneous improved degassing of undesired by-productscatalyst and deactivation of active catalyst sites, it is possible toprepare purer polymers containing less reaction by-products and havingimproved organoleptic properties and less color formation.

Also, it was surprisingly found that an emulsion of at least one organicperoxide and water is more effective than the individual componentsthereof and that removing organic volatile compounds and water vaporfrom the molten polymer drastically reduces any generated degradationand by-product in the polymer.

According to one or more embodiments, the emulsion may be added to thepolymer in such a manner that the amount of the at least one organicperoxide with respect to the amount of the polymer attains at apredetermined value. For example, the emulsion may be added to thepolymer so that the amount of the at least one peroxide added to thepolymer ranges from 100 ppm to 6000 ppm with respect to the amount ofthe polymer, where ppm, in the present disclosure and in the followingclaims, indicates mg of at least one organic peroxide feed/kg of polymerfeed. For example, when extruding is performed in an extruder, themethod, according to one or more embodiments, may further comprisefeeding the polymer and the composition to the extruder so that apredetermined ratio between the at least one organic peroxide-feed andthe polymer-feed (for example from 100 ppm to 6000 ppm, for example from1500 ppm to 5000 ppm, for example of from 2000 to 3000 ppm) is attained.

According to one or more embodiments, the emulsion may be added to thepolymer before the extrusion. According to one or more embodiments, theemulsion may be added to the polymer during the extrusion.

The emulsion of at least one organic peroxide and water may be forexample obtained by using one or more emulsifiers.

According to one or more embodiments, the method comprises extruding amolten polymer in the presence of an emulsion comprising, for exampleconsisting of, at least one organic peroxide, water and at least oneemulsifier.

According to one or more embodiments, the emulsion may be prepared byadding water to the organic peroxide and at least one emulsifier (or acombination of a plurality of emulsifiers) in a plurality of stages toensure that a homogeneous fluid is obtained after each addition. Also,after each addition step, the composition may be stirred.

Examples of emulsifiers which may be used to obtain a stable organicperoxide/water emulsion suitable for use in the method of the presentapplication may be selected from the group of polyethoxy phenols,alkylene oxide block-copolymers, ethoxylated fatty alcohols, ethoxylatedfatty acids, sorbitan fatty acid esters, sorbitol esters and combinationthereof.

According to one or more embodiments, the emulsifiers may be selectedfrom the group consisting of ethoxylated fatty alcohols and ethoxylatedfatty acids.

According to one or more embodiments, the emulsifier or the plurality ofemulsifiers may have a total HLB value of at least 6, for example of atleast 8. For example, the emulsifier or the plurality of emulsifiers mayhave a total HLB value of at least 9. For example, the emulsifier or theplurality of emulsifiers may have a total HLB value of from 6 to 20, forexample from 8 to 18.

According to one or more embodiments, the emulsion may have apredetermined total HLB (Hydrophilic-Lipophilic Balance), for example inthe range from 8 to 18, for example from 9 to 16.

According to one or more embodiments, the emulsion may have apredetermined average droplet size, such as for example an averagedroplet size (d₅₀) between 1 microns to 100 microns, for example between5 microns to 100 microns, for example between 10 microns and 80 microns,for example from 20 microns to 60 microns.

According to one or more embodiments, the emulsion may have apredetermined average droplet size and a predetermined HLB incombination.

Average droplet size may be determined by means known to one of ordinaryskill in the art, for example by means of light diffraction techniques.The above-mentioned exemplary values of average droplet size refer tod₅₀, which corresponds to the average diameter such that 50% of thevolume of the organic peroxide droplets in the emulsion has a diameterof less than d₅₀, measured by a Malvern Mastersizer 2000® at roomtemperature.

The HLB (Hydrophilic-Lipophilic Balance) refers to a HLB determinedaccording to the method described by Griffin in 1949 (Journal of theSociety of Cosmetic Chemists 1949, 1 (5): 311-26) and 1954 (Journal ofthe Society of Cosmetic Chemists 5 (4): 249-56). The HLB of anemulsifier is a measure of the degree to which it is hydrophilic orlipophilic, determined by calculating values for the different regionsof the molecule. The total HLB of an emulsion comprising a number ofcomponents may be calculated on the basis of the HLB of each of theemulsion components and of the concentrations thereof in the emulsion.

According to one or more embodiments, extruding may be performed in thepresence of one or more polymer additives. Exemplary additives maycomprise, for example, fillers, antioxidants, fungicides, bactericides,reinforcing agents, antistatic agents, heat stabilizers, UV-stabilizers,flow enhancers, colorants and other additives or processing aids knownto those skilled in the art.

According to one or more embodiments, extruding may be performed in anextruder at predetermined extrusion conditions suitable for extruding apolymer, such as for example at a predetermined extrusion temperatureand at a predetermined extrusion pressure. With reference to anextruder, unless otherwise indicated, in the present description and inthe following claims the exemplary extrusion temperatures and pressuresare intended to indicate the barrel temperatures and pressures.

For example, extruding may be performed at an extrusion temperature offrom 180° C. to 260° C., for example from 190° C. to 250° C., forexample from 190° C. to 240° C.

According to one or more embodiments, the extrusion conditions may varyalong the length of the extruder. For example, the extrusion temperaturemay increase or decrease along at least a portion of an extrusion path,which may extend along different extruder zones.

According to one or more embodiments, in each extruder zone, thetemperature may be set within a predetermined temperature range.

According to one or more embodiments, the extruder may comprise, in theorder, a feed zone, a solid conveying zone, a solid compression zone, amelting zone, a melt conveying zone, at least one decompression zone, amelt compression zone and a die zone. The feed zone feeds the polymerpowder into the extruder and may be kept at a predetermined temperatureto avoid that the polymer powder becomes sticky or melts and to ensurethat the peroxide does not start reacting. The solid conveying zonetransports the polymer powder towards the compression zone. The solidcompression zone pressurizes the polymer powder, while most of thepolymer is melted in the melting zone, and the melt conveying zone meltsthe last polymer particles and mixes to a uniform temperature andcomposition. The at least one decompression zone allows the moltenpolymer to be decompressed. The melt compression zone pressurizes thepolymer melt, and the die zone forms the molten polymer into the desiredshape for collection.

According to one or more embodiments, the extruder may also comprise afurther melting and/or a further compression zone arranged downstream ofthe at least one decompression zone and a further melt conveying zonearranged downstream of the further melting zone. The further compressionzone may serve to repressurize the melt to get the melt through theresistance of the screens and the die, and the further melt conveyingzone may serve to further mix to a uniform temperature and composition.

According to one or more embodiments, the extruder may comprise twodecompression zones. The two decompression zones may be separated by amixing zone or may be immediately adjacent decompression zones.

According to one or more embodiments, extruding is performed at atemperature of from 30° C. to 200° C., for example from 30° C. to 50°C., in the extruder feed zone.

According to one or more embodiments, extruding is performed at atemperature of from 160° C. to 220° C. in the extruder solid conveyingzone.

According to one or more embodiments, extruding is performed at atemperature of from 180° C. to 240° C. in the extruder solid compressionzone.

According to one or more embodiments, extruding is performed at atemperature of from 210° C. to 280° C. in the extruder melting zone.

According to one or more embodiments, extruding is performed at atemperature of from 210° C. to 260° C. in the extruder melt conveyingzone.

According to one or more embodiments, extruding is performed at atemperature of from 210° C. to 260° C. in the extruder decompressionzone.

According to one or more embodiments, extruding is performed at atemperature of from 180° C. to 260° C. in the extruder melt compressionzone.

According to one or more embodiments, extruding is performed at atemperature of from 180° C. to 280° C. in the extruder die zone.

According to one or more embodiments, the temperature profile along theextruder may comprise a combination of one or more of these exemplaryranges of temperatures in the different zones of the extruder.

According to one or more embodiments, the extrusion conditions maycomprise, for example, a feed zone temperature of from 30° C. to 200°C., for example from 30° C. to 50° C., a solid conveying zone of from180° C. to 220° C., a solid compression zone of from 180° C. to 220° C.,a melting zone temperature of from 210° C. to 280° C., a melt conveyingzone of from 210° C. to 260° C., a decompression zone temperature offrom 210° C. to 260° C., a melt compression zone temperature of from210° to 260° C., and a die zone temperature of from 180° to 280° C.

According to one or more embodiments, the extrusion conditions may varybefore and after the introduction of the emulsion in the extruder. Forexample, the extrusion conditions may comprise a first temperatureprofile before the introduction of the emulsion into the extruder and asecond, different temperature profile after the introduction of theemulsion into the extruder. For example, both profiles may have any ofthe exemplary values defined above. For example, after the introductionof the emulsion into the extruder, the melt conveying temperature and/orthe melt compression zone temperature and/or the temperature of anyother extruder zone may be reduced, for example of 10° C.-40° C. Forexample, after the introduction of the emulsion into the extruder, thedie zone temperature may be reduced, for example of 20° C.-60° C., aloneor in combination with a reduction of the temperature of any otherextruder zone. Independently from or in combination with a possiblevariation of the temperature along the length of the extruder, also theextrusion pressure may vary along the length of the extruder. Forexample, the extrusion conditions may comprise a feed zone pressure offrom 10 mbar to 50 mbar and a melt compression zone of from 30 bar to120 bar. The remaining zones may have pressures intermediate to theexemplary pressures of the feed zone and of the melt compression zone.

The extrusion conditions may further comprise an intensive mixing in theextruder. According to one or more embodiments, sufficient mixing may beobtained by setting the screw speed of the extruder within the range offrom 190 rpm to 270 rpm.

According to one or more embodiments, the at least one decompressionzone may comprise a venting zone, for example including at least onevent port or a plurality of vent ports. The at least one decompressionzone may, for example, be arranged about two-thirds down the extruderscrew. The decompression zone allows gases, such as moisture andvolatiles, to escape from the molten polymer through the venting zone,for example through one or more vent ports provided in the venting zone.

By using a vented extruder comprising at least one vent port, thepressure may be relieved in the at least one decompression zone and anytrapped gases may be drawn out by vacuum. With such an extruder, theApplicant has surprisingly found that the method for modifying therheology of a polymer according to one or more embodiments of thepresent disclosure provides both rheological modification and additionaleffects positively influencing the properties of polymers, for exampleof polyolefins. These effects include the deactivation of activecatalyst sites and improved polymer degassing beyond the expectation ofthe contribution of the water and organic peroxide individually. Thedeactivation of active catalyst sites and improved polymer degassing inturn result in purer polymers containing less reaction by-products andamount of volatiles, improved organoleptic properties, such as odor andtaste, and less color formation. Further, the water of the composition,when removed through the at least one vent port, extracts undesireddeactivated species and degradation products from the molten polymer.

According to one or more embodiments, removing is performed by ventingthe extruder, for example during extruding. Venting may be for exampleperformed through at least one vent or vacuum port, in an extruderventing zone. According to one or more embodiments, a plurality of ventports may be defined circumferentially around the barrel and/orlongitudinally along a portion of the barrel.

The vent port(s) may strip-off the reaction water and undesireddeactivation species by means of a predetermined vacuum (i.e.,subatmospheric pressure) to assure that no residual water is present inthe polymer.

According to one or more embodiments, removing is performed byestablishing a predetermined vacuum in the extruder venting zone or in aplurality of venting zones. In case of a plurality of venting zones,each venting zone may be provided in a corresponding decompression zoneof the extruder comprising a plurality of decompression zones. However,according to one or more embodiments, a plurality of venting zones maybe provided in each decompression zone of the extruder.

According to one or more embodiments, the predetermined vacuum is set tofrom 0 mbar to 800 mbar, for example from 200 mbar to 800 mbar, forexample from 300 mbar to 600 mbar, for example from 350 mbar to 550mbar. According to one or more embodiments, removing may be performed bysetting a predetermined vacuum pressure in the extruder decompressionzone comprising a venting zone. For example, the decompression zonevacuum pressure may be of from 0 mbar to 800 mbar, for example from 0mbar to 600 mbar.

When removing is performed by establishing a predetermined vacuum in anextruder venting zone, the Applicant has found that the VOCs may attaina level which may be reduced by at least 40% when compared to the levelof VOCs attainable at atmospheric pressure, at the same extrusionconditions applied to the same polymer in the presence of the sameemulsion.

For example, the subatmospheric pressure in the venting zone can bemaintained by attaching the at least one vent port to a tube leading toa vacuum pump or other known devices for producing vacuum.

According to one or more embodiments, the polymer may comprise apolyolefin. The polyolefin may be selected, for example, fromhomopolymers and copolymers of olefins, the olefin monomers having forexample from two to eight carbon atoms.

According to one or more embodiments, the polyolefin may be selectedfrom the group comprising polypropylene homopolymers, polyethylenehomopolymers, copolymers comprising propylene, copolymers comprisingethylene and combinations thereof. For example, the polyolefin may beselected from the group consisting of polypropylene homopolymers,propylene copolymers, polyethylene homopolymers and ethylene copolymers.

According to one or more embodiments, polyethylene, such as linearlow-density polyethylene (LLDPE), low-density polyethylene (LDPE), highdensity polyethylene (HDPE) as well as ethyl vinyl acetate copolymer(EVA) and polyolefinic elastomer (POE), may be used. According to one ormore embodiments, polyethylene homopolymers and copolymers, for examplehaving a density in the range from 0.88 g/cm³ to 0.96 g/cm³, may beused. Polyethylene homopolymers and copolymers may be manufactured byany known process.

According to one or more embodiments, polypropylene may be used,comprising homopolymers, random copolymers, block copolymers andterpolymers of propylene. Copolymers of propylene may comprisecopolymers of propylene with other olefins such as ethylene, 1-butene,2-butene and pentene isomers, and for example copolymers of propylenewith ethylene. Terpolymers of propylene may comprise copolymers ofpropylene with ethylene and one other olefin. Random copolymers, alsoknown as statistical copolymers, are polymers in which the propylene andthe comonomer(s) are randomly distributed throughout the polymeric chainin ratios corresponding to the feed ratio of the propylene to thecomonomer(s). Block copolymers are made up of chain segments consistingof propylene homopolymer and of chain segments consisting of, forexample, random copolymer of propylene and ethylene. Homopolymers,random copolymers and block copolymers may be manufactured by any knownprocess.

For example, the polymer may be a propylene homopolymer or copolymer.According to one or more embodiments, the propylene homopolymer orcopolymer, before the modification of the rheology, may have an initialMFR, measured according to ISO 1133 with a load of 2.16 kg at 230° C.,of about 0.2 to about 100 g/10 min, for example from 0.2 to 50 g/10 min,for example from 0.2 to 20 g/10 min.

In the following description and claims, if not otherwise indicated, theMFR is a MFR measured according to ISO 1133 with a load of 2.16 kg at230° C.

According to one or more embodiments, the propylene homopolymer orcopolymer, after the modification of the rheology with one or moreembodiments of the emulsion, may have a final MFR, of up to 5000% higherthan the initial MFR. According to one or more embodiments, the finalMFR may be of from 50 to 2000 g/10 min, for example of from 20 to 100g/10 min, for example of from 5 to 20 g/10 min.

According to one or more embodiments, the emulsion comprises 20% to 80%by weight of at least one organic peroxide, up to 15% by weight of anemulsifier, and water in quantity enough to complete the 100% of thecomposition total weight. For example, the emulsifier may be present inan amount up to 15% by weight, for example from 0.1% to 12% by weight,for example from 0.5% to 8% by weight, for example from 1 to 6% byweight, with respect to the total weight of the composition.

According to one or more embodiments, the emulsion may consist of anorganic peroxide, water and an emulsifier, for example in theabove-mentioned exemplary concentrations.

According to one or more embodiments, the emulsion may comprise from 25%to 75%, for example from 40% to 70%, for example from 55% to 65%, byweight of at least one organic peroxide, up to 15% by weight of anemulsifier, and water in quantity enough to complete the 100% of thecomposition total weight.

For example, a storage capacity of above 1000 L may be obtained atperoxide dilutions of around 50% by weight.

According to one or more embodiments, the at least one organic peroxidecontains less than 10% by weight of active oxygen with respect to thetotal weight of organic peroxide(s). For example, the at least oneorganic peroxide may contain less than 7%, for example less than 5%, byweight of active oxygen with respect to the total weight of organicperoxide(s).

According to one or more embodiments, the at least one organic peroxidecomprise at least one dialkyl peroxide, such as for example2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane-3, ditert-butyl peroxide,ditert-amyl peroxide; tert-butyl cumyl peroxide,di(tert-butylperoxy-isopropyl)-benzene, dicumyl peroxide,3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane,3,3,5,7,7-pentamethyl-1,2,4-trioxepane and combinations thereof.

According to one or more embodiments, polymer powder or pellets and theemulsion may be fed into the extruder, which may be for example a singleor twin-screw extruder, separately or in combination.

When fed in combination, the polymer powder or pellets and the emulsionmay be optionally premixed, for example at a temperature of from 30° C.to 40° C.

The polymer powder or pellets and the emulsion may be fed separatelyinto the extruder at predetermined feed rates. For example, the feedrate of the polymer may be set within the range of 2 to 500 kg/h for labextruders and within the range of 5 to 100 tons/h for industrialextruders, and the feed rate of the emulsion may be adjusted to obtain afinal pellet having a desired MFR.

According to one or more embodiments, the emulsion, when fed separatelyfrom the polymer, may be added to the extruder in a continuous manner orin a discontinuous manner, stepwise or gradually. For example, theemulsion may be added to the extruder according to a predeterminedfrequency.

According to one or more embodiments, the temperatures of the differentzones of the extruder, which may have the above-mentioned exemplaryranges of temperatures in a steady state, may be set at lower values,before the emulsion is introduced. For example, the temperatures of thedifferent zones of the extruder may be set within ranges of temperatureswhich are at least 10° C.-20° C. lower than the correspondingsteady-state extrusion temperatures. However, the emulsion may be alsointroduced after the temperatures of the different zones of the extruderhave attained the steady-state ranges of temperatures.

According to one or more embodiments, the emulsion feed rate into theextruder may be gradually increased up to a predetermined value, whichmay change as a function of the desired final MFR of the pellet. Thefinal MFR may be measured by means of an online rheometer, for examplemounted on the die zone of the extruder.

Before increasing the emulsion feed rate into the extruder to asteady-state value, the temperatures of the barrel and die may be eithermaintained at the same temperatures set before the emulsion isintroduced or may be further reduced, for example of further 10° C.-20°C.

According to one or more embodiments, the method may further compriseintroducing water in the extruder, separately from the water containedin the emulsion. In this manner, enhanced uniform deactivation may beobtained.

According to a further aspect thereof, the present disclosure relates toa method for modifying the rheology of a polymer, comprising: extrudinga molten polymer and a composition comprising at least one organicperoxide and water in emulsion form, and establishing a predeterminedvacuum, for example set in any of the exemplary ranges defined above, inat least one extruder venting zone. The emulsion may comprise at leastone emulsifier, for example as defined above with reference to the firstaspect of the disclosure.

According to a further aspect thereof, the present disclosure relates toa polymeric composition obtained by one or more of the embodiments ofthe method defined above. The polymeric composition may have less than4000 odor units/m³, for example less than 3000 odor units/m³, forexample less than 2000 odor units/m³.

The polymeric composition may be used to prepare different productapplications, such as for example molding, films and fibersapplications. Examples of product applications are injection and blowmolding products, such as for example injection and blow moldingproducts used for packaging and automotive application. Spunbondnonwoven and melt blown fibers applications, such as for example forhygiene, medical, automotive and geotextile applications, may also beexemplary applications for the polymeric composition.

According to a further aspect thereof, the present disclosure relates tothe use of a composition comprising at least one organic peroxide andwater in emulsion form for deactivating active catalyst sites in apolymer under extrusion conditions.

According to a further aspect thereof, the present disclosure relates tothe use of a composition comprising at least one organic peroxide andwater in emulsion form for reducing the content of volatiles organiccompounds in a polymer under extrusion conditions.

According to a further aspect thereof, the present disclosure relates tothe use of a composition comprising at least one organic peroxide andwater in emulsion form for reducing yellowing of a polymer underextrusion conditions.

According to one or more embodiments of each of said uses, the emulsionmay comprise at least one emulsifier.

For example, in each of the above-mentioned uses, which may performedalso in combination, the emulsion may be used in an extruder under oneor more of the extrusion conditions defined above with reference to themethod. The emulsion and the polymer may be any of the exemplaryemulsions and polymers described above.

DESCRIPTION OF EMBODIMENTS

The following examples of methods for modifying the rheology of apolymer are given for illustrating but not limiting purposes.

The examples show the degassing performance of the methods for modifyingthe rheology of a polymer according to embodiments of the presentdisclosure.

The examples also show the improved degassing performance obtained bythe methods according to embodiments of the present disclosure comparedto conventional methods using mineral oil diluted organic peroxidesolutions and to conventional pure organic peroxides. The examples alsoshow lower VOCs, lower Yellow Index and lower odor in polymers treatedin accordance with embodiments of the method of the present disclosure.

In the following examples, emulsions will be described for modifying therheology of a polypropylene and of a propylene random co-polymer underextrusion conditions. However, different polymers may be rheologicallymodified by the method of the present disclosure. Also, emulsions willbe described comprising one organic peroxide. However, a plurality oforganic peroxides may be used in accordance with one or more embodimentsof the method of the present disclosure. Further, also stabilizersand/or additional additives may be used in accordance with one or moreembodiments of the method of the present disclosure.

Each exemplary emulsion at a predetermined concentration was fed with anexemplary polymer powder or pellets through a hopper directly into anextruder comprising a vent port. Together with the emulsion and thepolymer powder or pellets, any stabilizers and/or additional additivesmay be also fed through the hopper into the extruder.

The exemplary polymer and the emulsion were extruded in the extruder atan extrusion temperature ranging from 190° C. to 260° C. The extrusiontemperature was varied along the length of the extruder. In theexamples, the feed zone was cooled with cooling water at a temperatureof 38° C., the solid conveying zone temperature was set at 190° C., thesolid compression zone temperature was set at 220° C., the melting zonetemperature was set at 240° C., the melt conveying zone temperature wasset at 240° C. in Example 1 and at 230° C. in Example 2, thedecompression zone temperature was set at 230° C., the melt compressionzone temperature was set at 240° C. in Example 1 and at 230° C. inExample 2, and the die zone temperature was set at 240° C. in Example 1and at 260° C. in Example 2.

Also the extrusion pressure was varied along the length of the extruder.In the example, the vacuum pressure in the decompression zone was set at400 mbar. The melt pressure in the melt compression zone was found to beof about 100 bar.

The polymer and the emulsion were mixed by the screw of the extruder.During the transportation of the polymer through the extruder, polymerdegradation occurred. Water and other volatile compounds were removedduring the extrusion by establishing a predetermined vacuum in anextruder venting zone provided in the decompression zone and comprisinga vent port. The vent port was maintained at a predetermined vacuum of400 mbar.

Indeed, when the position of the extruder vent port was reached, thewater, which, under extrusion conditions, is water vapor, was separatedfrom the molten polymer and exited the extruder through the vent portdue to the vacuum. The vented polymer exited the extruder through apelletizer in the form of pellets.

The removal of water vapor using the method of the present disclosurewas significantly improved.

As shown in the following, this improvement resulted in an improvedreduction of VOCs, an enhanced reduction of odors and an improved colorof the final polymer pellets.

The following methods were used to determine the properties reported inthe examples.

Melt Flow Rate (MFR) is the MFR measured according to ISO 1133 with aload of 2.16 kg at 230° C.

VOCs are analyzed using static headspace-gas chromatography analysisaccording to the standard described in VDA-277.

Color formation during the rheological modification of the polymer isdetermined by the Yellowness Index (YI) of the polymer pellets. Todetermine the Yellowness Index, a color determination according to ASTMD6290 with a Group I Spectrophotometer, the LabScan XE from Hunterlab,with a D65/10° arrangement of Illuminant/Observer is performed. A samplecup is filled to the top with pellets, placed on the sensor port andcovered with an opaque and light excluding cover. The measurementdelivers the Tristimulus values X, Y and Z. The calculation of theYellowness Index is done according to ASTM E313 by the followingequation: YI=100 (Cx X−Cz Z)/Y, where the coefficients Cx and Cz areselected according to the setting of Illuminant and Observer used forthe measurement of the Tristimulus values. For Illuminant D65 andObserver 10°, Cx is 1.3013 and Cz is 1.1498.

The odor is evaluated by an odor test accomplished according to thedynamic olfactometry analysis described in the European Standard EN13725 using 2 hours conditioning at 40° C. The results of the dynamicolfactometry are given in Odor units/m³. One odor unit corresponds to anodor level which 40 ppb of n-butanol releases in 1 m³ of neutral gas.

Example 1

Example 1 shows the improved degassing performance obtained byperforming an embodiment of the method the present disclosure comparedto a method using a conventional mineral oil diluted organic peroxidesolution.

Sample 1 is a standard mineral oil diluted organic peroxide solutionavailable under the commercial name TRIGONOX® 101-E50(2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane, 50% solution in mineraloil) from AkzoNobel N.V.

Sample 2 is an emulsion comprising 60% by weight of2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane, 35% by weight of water, 1%by weight of trimethyl nonyl polyethylene glycol ether, 1% by weightpolyoxyethylene (9) nonylphenylether and 3% by weight of the alkyleneoxide blockcopolymer Pluronic® P-65 (commercially available from BASF).Sample 2 has a total HLB of 15.

The polymer used for rheological modification is a standard propylenehomopolymer powder obtained from a commercial Novolen process. The MFRof the polypropylene powder was of 2 g/10 min.

In two different tests, the polypropylene powder and Samples 1 and 2,respectively, were fed in the hopper of a twin screw extruder fromBrabender with an L/D (extruder Length/screw Diameter) of 20 andprovided with a vent port in a decompression zone of the extruder.Additionally, in each test, a standard additivation package consistingof tris(2,4-di-tert-butylphenyl)phosphite (Irgafos 168® commerciallyavailable from Ciba), calcium stearate (Ligastar CA350® commerciallyavailable from Peter Greven) and pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (Irganox 10100commercially available from Ciba) was fed to the extruder.

Both tests were performed under the same conditions, as detailed in thefollowing. The feed rate of the polypropylene powder was 3 kg/h and theamounts of the peroxide fed to the extruder with respect to the amountof polypropylene fed to the extruder were adjusted to 400 ppm to obtaina final pellet MFR of 25 g/10 min, which corresponds to a feed rate forthe peroxide solution in Sample 1 of 2.4 g/h and a feed rate of 2.0 g/hfor the peroxide emulsion in Sample 2. The feed rate of the additiveswas adjusted to 3 g/h for Irganox 10100 and Irgafos 168® and to 1.5 g/hfor Ligastar CA350®. The vacuum applied on the vent port was set to 400mbar. The starting extrusion temperature setting was of 190° C. in theextruder solid conveying zone and was increased up to 240° C. in themelt compression zone and in the extruder die zone. Before introducingthe 400 ppm of peroxide into the extruder, the temperature setting inthe solid conveying zone was kept at 190° C. and the temperature settingin the melt compression zone and die zone was reduced from 240° C. to200° C. and 220° C., respectively.

Table 1 shows detailed data of the evaluation using Sample 1 and Sample2.

TABLE 1 Peroxide Polypro- Polypro- content pylene pylene in the powderMFR pellet MFR peroxidic [g/10 min] [g/10 min] composition before afterYellow [% by rheological rheological VOCs Index weight] modificationmodification [mVs] [—] Sample 1 50 2 25 820 9.2 (compara- tive) Sample 260 2 25 640 5.0

The results of the peroxidic rheological modification of thepolypropylene powder with a MFR of 2 g/10 min to a pellet with a MFR of25 g/10 min with the different compositions show that, at the sameactive oxygen concentration in the extruder and thus for the samerheological modification, a significant lower level of VOCs is attainedwhen using Sample 2 compared to Sample 1. The lower value for the YellowIndex of Sample 2 indicates lower color formation and hence improvedperformance of the method according to the present disclosure.

Example 2

Example 2 shows the improved degassing performance obtained byperforming a method according to an embodiment of the present disclosurecompared to a method using a conventional pure organic peroxide.

Sample 3 is a pure organic peroxide, namely TRIGONOX® 101(2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane) available from AkzoNobelN.V.

Sample 4 is an emulsion according to an example of the presentdisclosure comprising 25% by weight of(2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane), 70% by weight of water,1% by weight of trimethyl nonyl polyethylene glycol ether, 1%polyoxyethylene (9) nonylphenylether and 3% by weight of the alkyleneoxide blockcopolymer Pluronic® P-65 (commercially available from BASF).Sample 4 has a total HLB of 15.

The polymer used for the rheological modification is a propylene randomco-polymer in powder form with an MFR of 0.3 g/10 min, available fromPetroquimica Cuyo in Mendoza, Argentina.

In two different tests, the polymer pellets and Samples 3 and 4,respectively, were fed into the extruder hopper into the twin screwextruder of Example 1 at a feed rate of 3 kg/h for the polymer andapproximately 3 g/h for Sample 3 and 12 g/h for Sample 4 to obtain afinal pellet MFR of 20 g/10 min. This corresponds to an amount ofperoxide fed to the extruder with respect to the amount of polymer fedto the extruder of 1000 ppm for both Samples 3 and 4. Additionally, ineach test, a standard additivation package consisting oftris(2,4-di-tert-butylphenyl)phosphite (Irgafos 168 ® commerciallyavailable from Ciba), calcium stearate (Ligastar CA350 ® commerciallyavailable from Peter Greven) and pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxy-phenyl)propionate) (Irganox10100 commercially available from Ciba) was fed to the extruder.

Both tests were performed under the same conditions, as detailed in thefollowing. The feed rate of the additives was adjusted to 3 g/h forIrganox 10100 and Irgafos 168 and to 1.5 g/h for Ligastar CA350®. Thevacuum applied on the vent port was set to 400 mbar. The startingextrusion temperature setting was of 210° C. in the extruder solidconveying zone and was increased up to 230° C. in the melt conveyingzone and the melt compression zone and to 260° C. in the extruder diezone. Before introducing the peroxide into the extruder, the temperaturesetting in the solid conveying zone was kept at 210° C. and thetemperature settings in the melt conveying zone and melt compressionzone were decreased from 230° C. to 200° C.; the temperature setting inthe die zone was reduced from 260° C. to 210° C.

Table 2 shows details of the evaluation including the results of an odorevaluation.

TABLE 2 Polypro- Polypro- Peroxide pylene pylene content copolymercopolymer in the powder MFR pellet MFR peroxidic [g/10 min] [g/10 min]Odor composition before after concen- [% by rheological rheologicaltration weight] modification modification [OU/m³] Sample 3 100 0.3 205970 (comparative) Sample 4 25 0.3 20 1900

The results of the rheological modification using Sample 3 and Sample 4show that, at the same active oxygen concentration in the extruder thusfor the same rheological modification, a significant lower Odor unit percubic meter (OU/m³) is attained for the emulsion of Sample 4 compared toSample 3 consisting of a pure peroxide. The lower Odor unit per cubicmeter means that Sample 4 releases less odorous compounds and hastherefore an improved odor. While the invention has been described withrespect to a limited number of embodiments, those skilled in the art,having benefit of this disclosure, will appreciate that otherembodiments can be devised which do not depart from the scope of theinvention as disclosed herein. Accordingly, the scope of the inventionshould be limited only by the attached claims.

The invention claimed is:
 1. A method for modifying the rheology of apolymer, comprising: extruding a molten polymer and an emulsion, theemulsion consisting of at least one organic peroxide, at least oneemulsifier with a total Hydrophilic-Lipophilic Balance (HLB) valuebetween 6 and 16, and water removing volatile compounds generated duringextrusion from the molten polymer under extrusion conditions and under apredetermined vacuum; reducing both the content of volatile compoundsand yellowing of the molten polymer in the presence of the emulsion,wherein the volatile compounds comprise water and volatile organiccompounds resulting from the degradation of at least one of the organicperoxide or the polymer, and wherein removing volatile compounds isperformed by establishing the predetermined vacuum in at least oneextruder venting zone.
 2. The method of claim 1, wherein thepredetermined vacuum is set to from 0 mbar to 800 mbar.
 3. The method ofclaim 1, wherein the at least one extruder venting zone is provided inat least one extruder decompression zone.
 4. The method of claim 1,further comprising feeding the polymer and the emulsion so that theamount of the at least one peroxide feed ranges from 100 ppm to 6000 ppmwith respect to the amount of the polymer feed.
 5. The method of claim1, wherein the at least one organic peroxide contains less than 10% byweight of active oxygen with respect to the total weight of organicperoxide(s).
 6. The method of claim 1, wherein the at least one organicperoxide is selected from the group comprising dialkyl peroxides.
 7. Themethod of claim 1, wherein the at least one organic peroxide is selectedfrom the group comprising 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane-3,ditert-butyl peroxide, ditert-amyl peroxide, tert-butyl cumyl peroxide,di(tert-butylperoxy-isopropyl)-benzene, dicumyl peroxide,3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane,3,3,5,7,7-pentamethyl-1,2,4-trioxepane and combinations thereof.
 8. Themethod of claim 1, further comprising providing the emulsion from astorage having a capacity of greater than 1000 L for the extruding step.9. The method of claim 1, further comprising adding water to the moltenpolymer and emulsion mixture in the extruder, beyond the water containedin the emulsion, to further deactivate catalyst sites.
 10. The method ofclaim 1, wherein the emulsion consists of 20% to 80% by weight of the atleast one organic peroxide, 0.1% to 15% by weight of the at least oneemulsifier, and water in quantity enough to complete the 100% of theemulsion total weight.
 11. The method of claim 1, wherein the at leastone emulsifier is selected from the group comprising polyethoxy phenols,alkylene oxide block copolymers, ethoxylated fatty alcohols, ethoxylatedfatty acids, sorbitan fatty acid esters, sorbitol esters andcombinations thereof.